The present invention relates in general to apparatus for printing telephone messages, and more particulary to apparatus for printing telephone messages in accordance with Touch Tone signals.
The Touch Tone telephone system is rapidly becoming the standard system for the industry. In the Touch Tone telephone system, each of the tweleve keys on a Touch Tone pad of a telephone instrument corresponds to a discrete dual tone multiple frequency analog signal. The dual tone multiple frequency analog signal is transmitted over telephone lines to a central station. The dual tone multiple frequency analog signals control the switching logic circuits of a central station to establish telephone connections between subscribers. Once a connection is established between subscriber substations, the dual tone multiple frequency analog signals are used to transmit and receive data, such as alpha numeric symbols, punctuations and other characters.
The widespread availability of Touch Tone technology has made it possible for low cost data transmission devices to be used. Heretofore, such data transmission apparatus did not provide a permanent record of the transmitted data. Thus, a person was required to be present at the receiving station to copy down the data as it was received. Additionally, the lack of printed verification of the transmitted data increased the chances of error at the transmitting station and at the receiving station.
A Touch Tone receiver has been manufactured by Tone Technology Corporation of Sunnyvale, Calif., which processes 2-out-of-8 signal frequencies generated by a Touch Tone telephone to provide discrete output signals corresponding to the character selections. It provides binary coded decimal signals or discrete 1-out-of-16 signals.
Telaris Telecommunications, Inc. of Irvine, Calif., has manufactured a Touch Tone decoder, in which Touch Tone signals comprising sixteen telephone standard 2-of-8 codes are received, processed and output as logic levels or discrete pins. It provides binary coded decimal signals or discrete 1-of-16 signals. The dual tone input signals are buffered by a bridging input amplifier from which the dual tone input signals are separated by HI and LO pass filters. The separated HI and LO signals are squared by limiters for delivery to the HI and LO envelope detectors. The valid and invalid signals are secured by a speech detector and the relative level of the valid and invalid signals is monitored by comparator circuits. The HI and LO frequency signals are counted and decoded.
In the patent to Tunzi, U.S. Pat. No. 4,067,178 issued on Jan. 10, 1978, for Variable Frequency Waveform Synthesizer, there is disclosed a variable frequency waveform synthesizer in which a waveform at a desired frequency is repetitively generated with each cycle of the waveform generated at N discrete steps.
In the patent to Nilssen et al., U.S. Pat. No. 3,959,603, issued on May 25, 1976, for Dual Tone Multiple Frequency Receiver/Decoder, there is disclosed apparatus for separating two analog component signals which make up a dual tone multiple frequency signal. The component signals are converted into digital identification signals. The identification signals are recombined and develop a digital output signal which corresponds to the input signal. A digital logic circuit is responsive to the identification signals to produce 1-of-16 digital output signals which correspond to the touch tone signal input.